In these days, the development of optical fiber sensor technology is so remarkable that it can measure various physical and chemical quantities ranging from a few millimeters to over several kilometers. In addition, it is attempted to assess the structural integrity of the state of the advanced technologies and existing structures such as ships, aircrafts, and bridges. This paper introduced the case histories of the measuring technology of optical fiber applied on structures such as roads and tunnels. The case history using OTDR (Optical Time Domain Reflectometery) was also introduced in this paper. Measurement of the pre-convergence of a tunnel is essential to assess the safety of a tunnel and understand the geological conditions ahead of an advancing tunnel. Therefore, the pre-convergence measuring technology using OTDR is expected to substitute conventional measuring techniques.

Geothermal energy is believed to be an important source among the renewable energy sources to provide the base load electricity. Although there has been a drastic increase in the use of geothermal heat pump in Korea, there is no geothermal power plant in operation in Korea. Fortunately, the first EGS (Enhanced Geothermal System) Project in Korea has started in Dec 2010. This five year project is divided into two stages; two years for exploration and drilling of 3 km depth to confirm the minimum target temperature of 100 degrees, and another three years composed drilling 5 km doublet, hydraulic stimulation of geothermal reservoir with expected temperature of 180 degrees (40 kg/s) and construction of MW geothermal power plant in the surface. This EGS project would be a landmark effort that invited a consortium of industry, research institutes and university with expertises in the fields of geology, hydrogeology, geophysics, geomechanics and plant engineering.

Failure aspects of cut-slope, which induce the sequential collapses during the excavation stage, have been analyzed. Slope rock structures are investigated by examining the orientations and positions of discontinuity planes calculated based on the BIPS image inside the boreholes. Drilled core log has been also used to identify the structural defects. Clay minerals of swelling potentials are detected through XRD analysis. Numerical analysis for slope stability has been performed by utilizing the joint shear strength acquired from the direct joint shear test. Cut-slope collapse characteristics have been studied by investigating the posture of failure-prawn joint planes and the stability of tetrahedral blocks of different sizes. Cross-section analysis has been also performed to analyze the cut-slope behavior and to estimate the amount of reinforcement required to secure the stability of cut-slope. Behavior of reinforced cut-slope is also investigated by analyzing the slope monitoring data.

This study focuses on having a temperature and water pressure effects on the change of material properties of rocks. Granite and limestone specimens from Gagok Mine were thermally treated with predetermined temperatures of 200, 300, 400, 500, 600 and (excepting for limestone) to estimate the reduction of material properties of rocks caused by heat. Specific gravity, effective porosity, elastic wave velocity, uniaxial compressive strength, Young's modulus and Poisson's ratio for pre-heated specimens were measured. With increasing temperature, material properties of both rock specimens change sequentially. Significant changes of specific gravity, effective porosity and elastic wave porosity occur above for granite and for limestone. Changes of uniaxial compressive strength, Young's modulus and Poisson's ratio seem to be similar to those of physical properties. GSI of 500, 600 and specimens inferred by using uniaxial compressive strength and Young's modulus of preheated granite specimens is found to be 81, 66 and 58 each. In case of pre-heated limestone specimens of 400, 500 and , the corresponding GSI is 76, 71 and 65 each. 500, 600 and granite specimens and 400, 500 and limestone specimens were pressurized to 7.5 MPa and their effective porosity, elastic wave velocity, uniaxial compressive strength and Young's modulus were measured. The average value of material properties (mentioned above) of 500, 600 and granite specimens under water pressure compared with material properties of non-pressurized pre-heated specimens exhibits the reduction of 7.6, 11.3 and 14.9%, respectively. In case of 400, 500 and limestone specimens under water pressure, the average value of material properties decreases by 8.2, 13.8 and 21.9%, respectively.

This study is to estimate the uniaxal compressive strength (UCS) for the weak rocks using needle penetrometer test. The appropriate ratio of the artificial rocks for this test was cement (C):bentonite (B):water (W) = 1.3:0.7:2.3 or 1.5:0.5:2.0. From the relationship between needle penetration resistance (NPR) measured by needle penetrometer test and an estimated UCS, NPR and UCS tended to increase with increasing the curing period. Also from the relationship between the measured NPR and the measured UCS, NPR-UCS was linearly increased with the curing periods of 3-day to 14-day regardless of the ratio, then in the curing periods of 14-day to 28-day it was nearly constant. In conclusion, the overall relationship between NPR and UCS shows a linear relation for the most part, it means that UCS is possible to be estimated from NPR by needle penetrometer test in the case of weak rocks.

Analysis of correlation and behavior characteristics at elastic wave velocity have studied on Korean rock data after checking population size and Chi-square method. Behavior characteristics are quite different from each rock and mechanical parameters at elastic wave velocity. This study shows it is necessary to analize correlation to rock behavior characteristics for correct answer from natural rock.

In this study, it was aimed to develop a thermal-hydraulic-mechanical coupled fracture mechanics code that models a fracture initiation, propagation and failure of underground rock mass due to thermal and hydraulic loadings. The development was based on a 2D FRACOD (Shen & Stephasson, 1993), and newly developed T-M and H-M coupled analysis modules were implemented into it. T-M coupling in FRACOD employed a fictitious heat source and time-marching method, and explicit iteration method was used in H-M coupling. The validity of developed coupled modules was verified by the comparison with the analytical result, and its applicability to the fracture initiation and propagation behavior due to temperature changes and hydraulic fracturing was confirmed by test simulations.

Stereophotogrammetry is used to extract spatial information of an object by constructing a stereo-image from two or more photos. In this study, stereophotogrammetry was adopted for analyzing blast fragmentation of rock blocks in a quarry site. 2D image processing and stereophotogrammetry were applied to the fragmentation analysis of rock blocks horizontally scattered in a laboratory, and their results were compared with physical measurements using a water tank. Fragmentation of rock muckpiles was estimated in laboratory and field tests by using the stereophotogrammetry and statistical analysis.